Sophorolipids, formerly known as sophorosides, are glycolipid biosurfactants produced by yeast strains such as Starmerella (Candida) bombicola, Candida apicola, Candida bogoriensis, Candida batistae and Wickerhamilella domercqiae. They are composed of a disaccharide moiety linked to one hydroxyl group of one w or (w-1)-hydroxy fatty acid that is saturated or monounsaturated. The sugar moiety, i.e. sophorose or 2-O-glucopyranosyl-D-glucopyranose, may further show mono- or diacetylation at the 6′ and 6″ positions. The nature of the hydroxy fatty acid is characteristic, with the hydroxyl group being located on the n or n-1 carbon atom. The composition of the hydroxylated fatty acid varies depending on the production conditions. Lactonization frequently occurs between the carboxyl group and the 4″ OH group of the sophorose, providing sophorolactones in addition to sophorolipids in acid form. Hence, sophorolipids are considered as being a mixture of the compounds presented by the formula I, representing sophorolipids in lactone form, and by formula II, representing sophorolipids in acid form, in which 1. R′ and R″ represent hydrogen or an acetyl group, or 2. R′ is an acetyl group and R″″ a hydrogen group, or 3. R′ is hydrogen and R″ is an acetyl group, or 4. both R′ and R″ are hydrogen, or 5. both R′ and R″ are acetyl groups. The molecules of formula I are lactonic sophorolipids, also called sophorolactones. The molecules of formula II are open ring sophorolipids, also called sophorolipids in acid form. The carbon chain length n may range from 2 to 16 carbon atoms. Typically the carbon chain length is 16 to 18 carbons long; that is n=13-15.
Sophorolipids are typically produced by fermentation processes wherein a glycolipid producing micro-organism is fed with a sugar supply and a substrate under appropriate fermentation conditions for the production of the sought sophorolipids.

This process has the disadvantage that a group of numerous homologs is formed. Moreover the formation ratio of these homologs varies as a function of their substrate, e.g. a hydrocarbon source, as well as the fermentation conditions. The production of a product having a given ratio using a fermentation process is difficult. This also hampers product development as properties and function of the sophorolipid varies with ratios of the homologs.
It is known that the acetyl bonds in sophorolipids are chemically unstable and are very easily hydrolysed by heating or prolonged storage close to neutrality or even at ambient temperature under slightly alkaline conditions, which leads to the obtaining of the completely de-acetylated acid form. It is therefore extremely difficulty by fermentation or chemistry to obtain a single product and a fortiori an acetylated product.
Processes for the isolation of one of the main forms (acid or lactone) from sophorolipids have been investigated. The processes thus far described require extraction by alcohol, e.g. EP 209783, a process which is both long and expensive. Moreover extraction by a specific solvent does not always give good results, because the solubility of the homologues in a solvent differs significantly, which affects the quality of the products obtained. In addition, it is not desirable in view of the use of sophorolipids as biosurfactants. It is undesirable that the product contains traces of organic solvents, resulting from the separation process.
The lactone form of sophorolipids has been documented to be the most active sophorolipid type, both with regard to lowering surface tension and to antimicrobial activity.
Therefore there is a demand in the industry for an improved sophorolactone production process, which leads to less complex mixtures, is easy in use, provides a satisfactory yield, is economically feasible, and is environmentally friendly, e.g. less organic solvent use.
In the prior art, for instance EP1411111, a liquid sophorolipid mixture is formulated on an alkaline powder. This composition spontaneously hydrolysed during storage to sophorolipids in acid form. These acids are known for their increased foaming over sophorolipids in lactone form. As a result, the products produced increased amounts of foam when used. This is particularly undesirable in applications where foam formation needs to be controlled, for instance in automated dishwashers characterized by frequent mechanical actions. Hence, it would be desirable to obtain a sophorolactone composition with improved hydrolytic stability, and thus storage stability.
Furthermore, there is a demand in industry to obtain an economically feasible source of sophorolactone that allows the production of derivatives such as w or (w-1)-hydroxy fatty acids and/or sophorose on an economically relevant scale.
It is an object of the present invention to provide an improved process for the synthesis of sophorolactone and derivatives, that at least solves one of the problems of the prior art. It is a further object of the invention to provide sophorolactone compositions with improved properties, such as hydrolytic stability, increased ease of handling. It is also an object of the invention to provide a more economically friendly access to some uses of sophorolactone and its derivatives.